UPDATE 1-New breast cancer drugs block cell repair enzyme

* BiPar/Sanofi drug boosts survival 60 pct

* AstraZeneca's olaparib shrinks tumors in 1/3 of patients

* Other types of cancer might be candidates (Recasts first paragraph; adds reaction, application to other cancers, paragraphs 4 and 22)

By Deena Beasley

ORLANDO, Fla., May 31 (Reuters) - Drugs that block a cell repair enzyme known as PARP show promise as treatments for some of the most aggressive and difficult-to-treat forms of breast cancer, according to new research.

Mid-stage results from a PARP inhibitor developed by BiPar Sciences Inc show that it improved survival by 60 percent compared with chemotherapy alone for women with "triple negative breast cancer."

And a small trial of AstraZeneca Plc's (AZN.L: Quote, Profile, Research) olaparib as a stand-alone therapy in women with advanced breast cancer linked to genetic mutations showed that it shrank tumors in a third of patients.

"While still very preliminary, these are some of the most exciting results we have seen in a long time," said Dr. Eric Winer, breast cancer chief at Boston's Dana-Farber Cancer Center.

The findings were presented on Sunday at the annual meeting of the American Society of Clinical Oncology.